In various multistage turbomachines used for energy conversion, such as gas turbines, a fluid is used to produce rotational motion. Referring to FIG. 1, a gas turbine 10 is schematically shown. The turbine 10 includes a compressor 12, which draws in ambient air 14 and delivers compressed air 16 to a combustor 18. A fuel supply 20 delivers fuel 22 to the combustor 18 where it is combined with the compressed air 16 and the fuel 22 is burned to produce high temperature combustion gas 24. The combustion gas 24 is expanded through a turbine section 26, which includes a series of rows of stationary vanes and rotor blades. The combustion gas 24 causes the rotor blades to rotate to produce shaft horsepower for driving the compressor 12 and a load, such as an electrical generator 28. Expanded gas 30 is either exhausted to the atmosphere directly, or in a combined cycle plant, may be exhausted to atmosphere through a heat recovery steam generator.
The rotor blades are mounted to disks that are supported for rotation on a rotor shaft. Annular arms extend from opposed surfaces of adjoining disks to form pairs of annular arms each separated by a gap. A cooling air cavity is formed on an inner side of the annular arm pairs between the disks of mutually adjacent stages. In addition, a labyrinth seal may be provided on an inner circumferential surface of stationary vane structures that cooperate with the annular arms to form a gas seal between a path for the hot combustion gases and the cooling air cavity. Each annular arm includes a slot for receiving a seal strip, known as a “belly band”, which spans the gap between each annular arm pair to stop a flow of cooling air from the cooling air cavity into a path for the combustion gas 24. The seal strip may include multiple segments that extend in a circumferential direction and are interconnected at lapped or stepped ends.
During use, the seal strips may shift in a circumferential direction relative to each other. Shifting may cause one end of a segment to increase an overlap with an adjacent segment, while an opposite end of the segment will move out of engagement with an adjacent segment thus opening a gap for passage of gases through the seal strip. Therefore, an anti-rotation mechanism is provided for stopping circumferential shifting of seal strip segments.
An anti-rotation mechanism that is originally installed at the factory during assembly of a gas turbine exhibits wear after a prolonged period of turbine operation. In order to replace the anti-rotation mechanism with one of the same design, the rotor has to be de-stacked or disassembled which leads to undesirable downtime and increased cost for gas turbines that are currently in the field. Replacement anti-rotation mechanisms that do not require de-stacking of the rotor utilize welding operations to join mechanism components, require modification of a disk and/or are difficult to install. However, performing a welding operation or making modifications in the field is difficult and accidental welding of the disk during repair may occur.